Aluminum is conventionally produced by smelting in a Hall bath. During the smelting operation, it is desirable to control parameters such as the temperature of the bath and to determine the composition of the molten aluminum in the bath. However, the methods that are currently used to measure the alumina concentration and sodium fluoride to aluminum fluoride ratio (NaF:AlF.sub.3) of the bath are confined to laboratory batch tests. Such laboratory testing causes control measurements to be made several hours after sampling, with little indication of current process conditions.
A probe that measures the bath and liquidus temperatures of a Hall bath during processing has been developed by Heraeus Electro-Nite, and is commercially available under the designation Cry-O-Therm. The probe includes a single thermocouple that is submerged in the molten bath. The Cry-O-Therm vibrates the sample during cooling to cause nucleation of the bath during cooling. An abrupt change in the slope of the cooling curve while the sample is being vibrated is taken as the liquidus. The difference between the pot temperature and the liquidus is taken as the super heat of the bath. However, this type of probe does not measure the NaF:AlF.sub.3 ratio, which is critical for accurately determining the liquidus and alumina concentration.
The present invention has been developed in view of the foregoing and to address other deficiencies of the prior art.